1. Field of the Invention
The present invention relates to a diversity antenna and, more particularly, to a flat type diversity antenna suitable for movable communication.
The present invention also relates to a flat type diversity antenna capable of covering a plurality of frequency bands.
2. Description of the Related Art
A mobile communication system, e.g., a mobile telephone, employs various types of diversity schemes, e.g., space diversity, power density receiving, and polarization diversity schemes, in order to prevent the influence of fading caused by complex topography and obstacles.
According to the conventional space diversity scheme, antennas having the same polarization are arranged at positions spatially phase-shifted from each other by 90.degree., and a signal from an antenna in a good condition is selectively used. Since two antennas are arranged at positions phase-shifted from each other by 90.degree., the installation space is increased.
According to the power density receiving scheme and the polarization diversity scheme, a slot antenna and a monopole antenna are combined. Since two antennas are arranged at spatially the same position, the entire antenna size is increased.
Hence, a conventional diversity scheme antenna is not suitable for mobile communication that needs a small antenna.
As the use of mobile and portable telephones has been spreading remarkably, a single frequency band is becoming insufficient to hold a necessary number of circuits. Hence, a telephone service using a plurality of frequency bands has been studied in the mobile telephone system and the like.
However it is inconvenient and requires the installation space to provide antennas to movable bodies in units of frequency bands. Also, it is difficult to completely cover the plurality of frequency bands by a conventional single antenna.